1. Field of the Invention
The present invention relates to an assembly process for connecting two electronic components to each other, of the vertical connection type more commonly called the “flip-chip” process, according to which one of the two electronic components is flipped to enable vertical electrical connections or assemblies to be made.
The invention makes it possible to obtain an assembly between electronic components whatever their interconnect pitch and the gap between these components.
The invention more particularly relates to the assembly between a chip and a substrate, for example both made of silicon.
The invention aims to control the final gap between electronic components once the assembly is produced.
In the context of the invention “assembly process for connecting two electronic components to each other” will be understood to mean either an assembly of two components of different materials or an assembly of two components made of the same material. In particular, an assembly according to the invention may relate to an assembly between an electronic chip and a substrate, both possibly being made from silicon.
The expression “interconnect pitch” refers to the distance between two connection pads on the same electronic component.
The expression “gap between components” refers to the distance between two opposing components, defined by the interconnection height.
2. Description of Related Art
The so-called “flip-chip” technique is a well-known technique for mechanically and electrically interconnecting, or assembling, two components such as a chip and a printed circuit board. This technique called the “flip-chip” technique because one of the components, generally the chip, which carries conductors, is flipped to bring the two components face-to-face in order to allow interconnections to be formed by joining the conductors and metallic bumps, and contacts to be produced on the other component, generally a printed circuit board.
Where this technique is concerned, efforts are constantly being made to reduce the gap between components while allowing for an ever higher number of connections. Currently, the three main known categories of assembly using this technique—soldering, thermocompression bonding and the use of adhesives, such as ACFs (anisotropic conductive films)—each have their own limitations when it comes to reducing the gap.
In particular, low-temperature thermocompression with penetration of conductive inserts into bumps, such as described in the patent application WO 2006/054005, is limited by the very large force that is required to establish a very high number of connections, and by virtue of the feasibility of production of the inserts themselves.
Thus, to overcome the limitations of this process, the Applicant has proposed in patent application WO 2009/115685 to produce conductive inserts in the form of blind-tubes of which the base is securely fastened to the area of a component. Conductive inserts were the subject of an improvement patent application EP 2 287 904 with at least one area of the open end of an insert left free in order to allow gases contained in the insert to escape during insertion. This patent provides various new shapes for the conductive inserts such as open bar, elements with star-shaped or cruciform cross sections, lobed etc. Although broadly satisfactory in terms of the required force level and feasibility of production of the inserts, the process according to these patent applications could still be improved upon.
More particularly, the inventors of the present application have sought a solution that will make it possible to control with certainty and great precision the gap between two components to be hybridized using a low-temperature thermocompression process, and to avoid any risk of electrical short-circuits between the conductive inserts of one component and the connection pads of the other component.
It is already known in the art concerning the “flip-chip” technique to use various types of spacers, i.e. spacers that allow a constant gap to be maintained between components.
Patent applications FR 2 694 841, US 2003/0038157 and WO 93/06964 implement a soldering process and disclose the use of spacers the constituent material of which, has a higher melting point than the interconnect bumps in order to remain solid during the melting, commonly called reflow, of said interconnect pads.
Patent application US 2005/0104222 proposes to use spacers in the form of discontinuous strips which are reflowed at the same time as the interconnect bumps. Here the spacers are produced to compensate for stresses caused by thermal expansion during operation.
Patent application JP 3 030 349 proposes to produce spacers in the form of drops of an adhesive, such as a silicone adhesive, injected by syringe, which drops make it possible to absorb some of the stresses created during reflow of the interconnect bumps, while also guaranteeing the gap between chips.
Patent application WO 2011/018572 proposes to use spacers taking the form of balls at the ends of the components, an insert secured to one of the components being inserted into each ball. The spacers have a height that must be greater than a hermetic strip arranged internally to the spacers, in order to seal bolometer support studs. The spacers formed by the balls are plastically deformed during assembly of the components.
Patent application FR 2 928 032 proposes to use spacers level with each buried interconnect track in which a tip is inserted. These spacers of conductive and ductile material support the tips and have a height that makes it possible to locally control the penetration of the tip into the buried track, thereby avoiding the use of an adhesive.
Patent application US 2010/079631 relates to a process for manufacturing an imaging device and proposes joining components together by the inserting pins into a plastically deformed material. Spacers are placed between each contact pad of ductile material on each of the components in order to prevent the pins from passing right through the ductile pads. A significant drawback is that the spacers of components that must bear against each other must be perfectly aligned with each other. In addition, here the spacers are located on both faces of the components, which spacers are made from a different material to the interconnections themselves: they must therefore be perfectly aligned to be useful. Systematically placed between the connections, they limit the minimum distance between two connections, i.e. they limit the pitch.
The general aim of the invention is to propose an improvement of the assembly process according to aforementioned patent applications WO 2009/115686 and EP 2 287 904 and which palliates at least some of the drawbacks of the prior art mentioned above.
One particular aim of the invention is to propose a solution allowing the gap between two microelectronic components assembled using a low-temperature thermocompression process to be controlled with certainty and great precision, and any risk of electrical short-circuit between the conductive inserts of one component and the connection pads of the other component to be avoided.